x86/hvm: fix interaction between internal and external emulation

A call to handle_hvm_io_completion() is needed for completing I/O
that requires external emulation. Such completion should be requested when
hvm_vcpu_io_need_completion() returns true after hvm_emulate_once() has
completed. This is indicative of the underlying I/O emulation having
returned X86EMUL_RETRY and hence a re-emulation of the instruction is
needed to pick up the result of the I/O.

A call to handle_hvm_io_completion() is NOT needed when the underlying
I/O has not returned X86EMUL_RETRY since there will be no result to pick
up. Hence it bogus to request such completion when mmio_retry is set,
since this can only happen if the underlying I/O emulation has returned
X86EMUL_OKAY (meaning the I/O has completed successfully).

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>

diff --git a/xen/arch/x86/hvm/io.c b/xen/arch/x86/hvm/io.c
index e449b4196e49eff907acd41d620f2711e523531e..9d9e1b0e4083e671d80a727423eef231040b524c 100644 (file)
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -88,7 +88,7 @@ bool hvm_emulate_one_insn(hvm_emulate_validate_t *validate, const char *descr)
 
     rc = hvm_emulate_one(&ctxt);
 
-    if ( hvm_vcpu_io_need_completion(vio) || vio->mmio_retry )
+    if ( hvm_vcpu_io_need_completion(vio) )
         vio->io_completion = HVMIO_mmio_completion;
     else
         vio->mmio_access = (struct npfec){};

diff --git a/xen/arch/x86/hvm/vmx/realmode.c b/xen/arch/x86/hvm/vmx/realmode.c
index 03dea6c0fcf2a530daa2fe694adf19808cb86ab2..11211c8cd897a87d2d86a3ce3d9e9c4804c45e67 100644 (file)
--- a/xen/arch/x86/hvm/vmx/realmode.c
+++ b/xen/arch/x86/hvm/vmx/realmode.c
@@ -103,7 +103,7 @@ void vmx_realmode_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt)
 
     rc = hvm_emulate_one(hvmemul_ctxt);
 
-    if ( hvm_vcpu_io_need_completion(vio) || vio->mmio_retry )
+    if ( hvm_vcpu_io_need_completion(vio) )
         vio->io_completion = HVMIO_realmode_completion;
 
     if ( rc == X86EMUL_UNHANDLEABLE )